This invention relates to a temperature control system for a thermal printer which prints on heat-transfer paper of the like using a printing plate with type. More particularly, this invention relates to a temperature control system which allows a rapid initial temperature rise of the printing plate, and which maintains the printing plate at a constant temperature after such a rapid temperature rise so that clear printing may be performed at any time.
Recently there has been increased usage of thermal printers for labeling various goods. One type of thermal printer is used to print prices, manufacturing dates and/or bar codes or the like on labels sequentially adhered on a tape-like base sheet and preprinted with additional information such as store names and addresses. Another type of prior art thermal printer is provided in a printing plate with a heater and type for printing store names, addresses or the like. The latter thermal printer may also print price and date information or may be disposed next to a thermal head that prints price and date information.
Unlike a thermal head having a number of small printing elements, the printing plate of a thermal printer of the type described above has a large surface area to be heated. Therefore, when a low voltage is applied to the heater, it takes a considerable period of time before the temperature of the printing surface is raised to a minimum temperature to obtain satisfactory printing. Thus, printing cannot be started immediately. Conversely, when a high voltage is applied to the heater, the time required to start printing is shortened. However, temperature control is difficult so that the printing surface of the printing plate may be overheated, burning the labels or causing unclear printing.